Wi-Fi technology has its origins in a 1985 ruling by the U.S. Federal Communications Commission that released the bands of the radio spectrum at 900 megahertz (MHz), 2.4 gigahertz (GHz), and 5.8 GHz for unlicensed use by anyone. Technology firms began building wireless networks and devices to take advantage of the newly available radio spectrum, but without a common wireless standard the movement remained fragmented, as devices from different manufacturers were rarely compatible. Eventually, a committee of industry leaders came up with a common standard, called 802.11, which was approved by the Institute of Electrical and Electronics Engineers (IEEE) in 1997. Two years later a group of major companies formed the Wireless Ethernet Compatibility Alliance (WECA, now the Wi-Fi Alliance), a global nonprofit organization created to promote the new wireless standard. WECA named the new technology Wi-Fi. Subsequent IEEE standards for Wi-Fi have been introduced to allow for greater bandwidth. The original 802.11 standard allowed a maximum data transmission rate of only 2 megabits per second (Mbps); 802.11n, introduced in 2007, has a maximum rate of 600 Mbps.
Under the IEEE Wi-Fi standards, the available frequency bands are split into several separate channels. These channels overlap in frequency, and therefore Wi-Fi uses channels that are far apart. Within each of these channels, Wi-Fi uses a “spread spectrum” technique in which a signal is broken into pieces and transmitted over multiple frequencies. Spread spectrum enables the signal to be transmitted at a lower power per frequency and also allows multiple devices to use the same Wi-Fi transmitter. Because Wi-Fi signals are often transmitted over short distances (usually less than 100 metres [330 feet]) in indoor environments, the signal can reflect off walls, furniture, and other obstacles, thus arriving at multiple time intervals and causing a problem called multipath interference. Wi-Fi reduces multipath interference by combining three different ways of transmitting the signal (in a method developed by Australian engineer John O’Sullivan and collaborators). The popularity of Wi-Fi has grown steadily. Wi-Fi allows local area networks (LANs) to operate without cables and wiring, making it a popular choice for home and business networks. Wi-Fi can also be used to provide wireless broadband Internet access for many modern devices, such as laptops, smartphones, tablet computers, and electronic gaming consoles. Wi-Fi-enabled devices are able to connect to the Internet when they are near areas that have Wi-Fi access, called “hot spots.” Hot spots have become common, with many public places such as airports, hotels, bookstores, and coffee shops offering Wi-Fi access. Some cities have constructed free citywide Wi-Fi networks. A version of Wi-Fi called Wi-Fi Direct allows connectivity between devices without a LAN. Radiotelegraphy, radio communication by means of Morse Code or other coded signals. The radio carrier is modulated by changing its amplitude, frequency, or phase in accordance with the Morse dot-dash system or some other code. At the receiver the coded modulation is recovered by an appropriate demodulator and the code groups are converted into the corresponding symbols. In many instances the symbols are generated by a computer and modem rather than with a manual telegraph key.
Chloroplasts are <em>chlorophyll-containing, eukaryotic cell structures</em> that function in photosynthesis by absorbing energy from sunlight, combining this energy with water and CO2 to convert them to sugars . This cell structure is known as a plastid. The sugars produced, are important for the survival of the plant.
Chloroplasts reproduce on their own, independent of the whole cell because they contain their own DNA. Plant chloroplasts are located in guard cells in plant leaves. Closely linked to these guard cells are tiny pores called stomata, which allow gas exchange required for photosynthesis.
Photosynthesis occurs in two stages:
The light reaction stage
The dark reaction stage
The Light reaction stage takes place in the presence of light. Clorophyll converts light into chemical energy in the form of ATP and NADPH. Both molecules produced, are used in the dark stage to produce sugar.
In the dark reaction stage, the stroma, containing enzymes, facilitates reactions leading to the production of sugars from ATP and NADPH. This process is also called the carbon fixation stage. The sugar produced can be stored in the form of starch for other processes such as respiration.
This happens because of the different genetic makeup or genotype of different individuals. The divergence mechanism occurs because of divergent evolution where in some cases random chances occurs and neurons became a source of stimulus for one but not other and vice versa.
